The chlorination of isoprene under normal conditions is less than straightforward and results in the formation of a variety of products. In a simple addition reaction involving loss of one double bond, dichlorides are formed such as 1,4-dichloro-2-methyl-2-butene and 1,2-dichloro-2-methyl-3-butene. A competing reaction, however, is one of substitution rather than addition in which a hydrogen ion is given up resulting in the formation of monochlorides such as 2-chloromethyl-1,3-butadiene and 1-chloro-2-methyl-1,3-butadiene. The substitution reaction produces HCl as a by-product which in turn reacts with unreacted isoprene in an HCl addition reaction to give hydrochlorides or monochlorobutenes such as 1-chloro-3-methyl-2-butene and 2-chloro-2-methyl-3-butene. In the preparation of the dichloride addition products, the formation of these monochloride substitution and HCl addition products constitutes an undesirable loss. Chlorination under conditions reported in the literature was found to result in discouragingly low weight yields of the 1,4- and 1,2-dichlorides, e.g., less than 50-60%, based on the weight of isoprene consumed. On a theory yield basis, which is moles of dichloride product per mole of isoprene consumed, this amounts to a yield of less than about 25-30%.